Internal structure and permafrost distribution in two alpine periglacial talus slopes, Valais, Swiss Alps

• Published in: Geomorphology (Amsterdam, Netherlands) Netherlands), 2011-09, Vol.132 (3), p.208-221
• Main Authors: Scapozza, Cristian, Lambiel, Christophe, Baron, Ludovic, Marescot, Laurent, Reynard, Emmanuel
• Format: Article
• Language: English
• Subjects: Alps; Borehole drilling; Boreholes; drilling; Earth sciences; Earth, ocean, space; electrical resistance; Electrical resistivity; Electrical resistivity tomography (ERT); Exact sciences and technology; Freezing; Frozen; Geomorphology, landform evolution; Geophysics: general, magnetic, electric and thermic methods and properties; ice; Internal geophysics; Marine and continental quaternary; Permafrost; sediments; Slopes; Stratigraphy; Surficial geology; Swiss Alps; Talus slope; temperature; tomography
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/j.geomorph.2011.05.010

In order to determine the spatial extension and the characteristics of permafrost within alpine talus slopes, two sites located in the western part of the Swiss Alps were studied using borehole drilling and electrical resistivity tomography (ERT) profiles. Three boreholes were drilled along an upslope–downslope transect in both talus slopes. In both sites, frozen sediments are present only in the two lowest boreholes, whereas the upper borehole does not present ice. This stratigraphy is confirmed by ground temperatures registered in the boreholes. In each site, three upslope–downslope ERT profiles were crossed with five, respectively four horizontal ERT profiles. All the upslope–downslope profiles show a difference in resistivities between the upper and lower parts of the slope, where a large resistive body with values higher than 35 kΩm is present. In the uppermost part of the profiles, the resistivities are lower than 10–15 kΩm. The borehole data allowed the stratigraphy obtained from the ERT inverted profiles to be validated, with regards to the distribution of frozen sediments as well as the depth of the detected structures. The results confirm that, in the two studied sites, permafrost is present in the lower sections of the talus slopes, whereas it is absent in the upper parts. Finally, the analysis of the talus structure showed that the permafrost stratigraphy, and in particular the ice content, may be an important element of interpretation of the palaeoclimatic significance of an alpine talus slope. ► Study of the spatial extension of permafrost in alpine talus slopes. ► Description of the stratigraphy of alpine periglacial talus slopes. ► Permafrost is present in the lower part of a talus slope but absent in the upper part. ► Palaeoclimatic interpretation of the permafrost stratigraphy of a talus slope. ► Collection of crossing ERT profiles to discriminate lateral effects.